Enhanced two-stage reactive polymer network forming systems

Abstract

In this study, we develop thiol/acrylate two-stage reactive network forming polymer systems that exhibit two distinct and orthogonal stages of curing. Using a thiol-acrylate system with excess acrylate functional groups, a first stage polymer network is formed via a 1 to 1 stoichiometric thiol-acrylate Michael addition reaction (stage 1). At a later point in time, the excess acrylate functional groups are homopolymerized via a photoinitiated free radical polymerization to form a second stage polymer network (stage 2). By varying the monomers within the system as well as the stoichiometery of the thiol to acrylate functional groups, we demonstrate the ability of the two-stage polymer network forming systems to encompass a wide range of properties at the end of both the stage 1 and stage 2 polymerizations. Using urethane di- and hexa-acrylates within the formulations led to two-stage reactive polymeric systems with stage 1 Tgs that ranged from −12 to 30 °C. The systems were then photocured, upon which the Tg of the systems increases by up to 90 °C while also achieving a nearly 20 fold modulus increase.

Functional off-stoichiometry thiol-ene-epoxy thermosets featuring temporally controlled curing stages via an UV/UV dual cure process

“…Samples were tested within 1 h after the first cure. During measurements, the temperature was ramped from room temperature (24)(25) C) to a constant temperature of 28 C over three hours. Each sample was measured under dark conditions using a vertical tension film mode at 15 lm amplitude and 1 Hz frequency oscillation.…”

“…13(a,b)]. After 4 days in water at 85 C the thiol-ene-epoxy samples results in a 10% reduction in storage modulus at 25 C, and in a < 10 C reduction of the T g . The broadening of the tan delta curves [ Fig.…”

“…P. Nair et al recently demonstrated very promising twostage thiol-acrylate systems. 25 These systems were formulated with a large excess of acrylate functionality polymerized in a first step via a Michael addition type thiol-acrylate "click" reaction. The resulting thiol-acrylate matrix then also contained unreacted acrylates, which enabled the polymer to first attain a soft state suitable for processing.…”

Fabrication and Characterization of Novel High Modulus, Two‐Stage Reactive Thiol‐Acrylate Composite Polymer Systems

“…[3,4] polymer system, to engineer polymer networks that have a distinct initial set of properties after a polymerization reaction that is self-limiting and a distinct second set of final properties that are achieved oncommand by photoinitiating a second polymerization reaction that does not occur at all during the first reaction and is orthogonal to the initial reaction. [5,6] The general concept of the two-stage reactive polymer system is shown in Figure 1. Previous studies have shown the advantages of a step-wise approach; [7,8] in this study to enable these two stable and distinct reaction stages to occur within the same polymer network, an amine catalyzed thiol-acrylate Michael addition reaction was used to form the initial polymer matrix.…”

“…[12][13][14] In our previous work, we exploited the ability to incorporate excess acrylate functional groups to enable greater versatility of these systems. [5,6] In this manner, after the initial Michael addition reaction, residual acrylate groups are pervasive throughout the polymer network yet stable in the absence of a radicalgenerating trigger. At a later time, the remaining acrylate functional groups are photopolymerized to form highly crosslinked polymer networks with mechanical performance much different from the initial polymer network.…”